1. Field of the Invention
The present invention is directed to a screw tap.
2. Description of the Prior Art
Known from DE 1676426 U are screw taps having a central drive portion with a square cross section, so that the drive torque necessary for the cutting forces can be reliably transmitted from the tap wrench to the screw tap by the principle of positive locking to the drive portion. Such screw taps are used, for example, as manual screw taps, and are expediently driven by hand with a tap wrench. It is to be considered a particularity that the known screw tap has a respective cutting portion on each of the two sides of the drive portion. Also known are screw taps implemented as manual or machine screw taps that are provided endwise with a square pin and a cutting portion attached thereto.
DE 91 14 307 discloses a screw tap in which the drive portion is shaped as a hexagon. A screw tap of this kind can thus be readily inserted in a standard drilling machine chuck and, moreover, can also be used as a bit with a commercial hand power drill. For this purpose, the hexagonal pin is also provided with retaining notches that make it possible for a screw tap of this kind to be locked in place in the hexagonal socket of the hand power drill.
Known from U.S. Pat. No. 2,408,565 are disk-shaped screw taps provided with a central square hole for receiving a square pin of a drive portion disposed at the end of a shaft that is separate from the screw tap.